River Information:

Rivers are usually oligotrophic poor in nutrients at their headwaters (where they originate) and eutrophic as they near the sea (at their estuary). Rivers are found worldwide from the frozen rivers at the south pole to the tropical rivers like the Amazon. River levels fluctuate with rainfall patterns, with some rivers drying completely in the dry season. River temperatures fluctuate with the seasons and are NOT vertically stratified like temperatures are in lakes and ponds (due to the mixing of the flowing water). The major producers include algae and riverside plants like the water willow, baldcypress, marsh marigold, cattails, and other wetland plants. River animals include birds like the kingfisher and bald eagle, fishes like the bass, sunfish, minnows, catfish, and gar.

Blue Nile Falls, in Africa, after heavy rains. Waterfalls dramatically oxygenate the water that flows over them.

By Giustino [CC-BY-2.0], via Wikimedia Commons

The Missouri, Mississippi and Illinois River confluence before and during the flood of 1993.

By Pierre cb (NASA Earth Observatory)[see page for license], via Wikimedia Commons

Glaciers - the birthplace of many streams.
By Mark Oliver Dittrich. Released into public domain on his behalf. (Digital camera.) [Public domain],
via Wikimedia Commons

A small oligotrophic mountain stream.

By César González Palomo from Madrid, Spain (P1020778 Uploaded by stegop) [CC-BY-SA-2.0], via Wikimedia Commons

A eutrophic canal.

Matthew Smith [CC-BY-SA-2.0], via Wikimedia Commons

Rivers and streams are found wherever there is enough rainfall runoff or snow melt to run off and create a channel.